Processes for treating raw sewage with channelled algae ponds are known. Exemplary of the known prior art processes is U.S. Pat. No. 3,462,360 entitled "Waste Treatment". An additional patent representing the state of the art is U.S. Pat. No. 2,867,945 entitled "Process of Photosynthetic Conversion of Organic Waste by Algal-Bacterial Symbiosis".
The known prior art algae-bacterial processes for treatment of sewage depend entirely upon algal photosynthetic reactions occurring during the daylight hours. In many of the prior art systems, although there is a constant flow of influent into the pond and effluent out of the pond, there is not a regulated flow of sewage throughout the channels of the pond during exposure to sunlight. Thus, these ponds are considered to be stagnant during exposure and treatment by sunlight. With this arrangement, where there is no regulated flow of the sewage in the pond channels, there is an inefficient transfer of oxygen to the bacterial phase.
An important part of the photosynthetic reaction which occurs in the algae pond during daylight hours is the production of oxygen. In fact, in accordance with the present invention, it has been discovered that enough oxygen can be dissolved in the algae pond because of the photosynthetic conversion of the waste to enable the utilization of an autoflotation unit without pressurizing dissolved air. Prior to the present invention, the amount of oxygen produced in the algae pond has been low and could not replace the pressurized dissolved air needed for flotation. Furthermore, in the prior art systems no oxygen is added to the system during the non-daylight hours.